The present invention relates to the use of the 2,6-disubstituted piperidines, cis-2,6-di-trans-styrylpiperidine and trans-2,6-di-trans-styrylpiperidine, as modulators of nicotinic acetyl-choline receptor mediated neurotransmitter release, uptake and storage. The 2,6-disubstituted piperidines of the present invention can be used for the treatment of drug abuse and withdrawal therefrom, as well as for the treatment of eating disorders such as obesity, and other neuropathologies.
Currently, drug discovery is focusing on neuronal nicotinic receptors (nAChRs) as novel targets for the development of therapeutic agents for a wide variety of central nervous system (CNS) diseases including, drug addiction, neuroendocrine, neuropsychiatric and neurological diseases, memory and learning disabilities, eating disorders, and the control of pain, as well as cardiovascular and gastrointestinal disorders. Nicotinic receptor antagonists have good potential as therapeutic agents, since they offer another means of modulating nicotinic receptor function. Nicotinic agonists rapidly desensitize these receptors, essentially inhibiting their function. Thus, inhibition of nicotinic receptor function may be the action, which confers clinical utility, indicating that nicotinic receptor antagonists could also be beneficial in the treatment of diseases for which nicotinic agonists are currently being developed. For example, schizophrenia and drug abuse have both been associated with hyperactivity of CNS dopaminergic systems, and inhibition of nicotinic receptors may be advantageous in reducing such hyperactivity. Furthermore, the availability of subtype-selective nicotinic receptor antagonists will be invaluable agents in both basic and clinical research, with regard to both the treatment and diagnosis of disease. Finally, subtype-selective antagonists will define the role of specific nicotinic receptor subtypes in both physiological function and disease states.
The action of many neuropharmacologically therapeutic agents involve the modulation of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) release, uptake and storage within its respective terminals in the central nervous system (CNS). Most neurotransmitters are stored in synaptic vesicles, which are prominent features of nerve terminals. Concentration into vesicles appears to be responsible for maintaining a ready supply of neurotransmitter available for neuronal exocytotic release into the synaptic cleft. Vesicles also serve the role of protecting the neurotransmitter from metabolic breakdown. One transport site on the vesicle membrane is the vesicular monoamine transporter-2 (VMAT2), whose role is to transport transmitter from the cytosol into the synaptic vesicle. Methoxytetrabenazine (MTBZ) has been used as a radiolabel to probe the interaction of drugs with VMAT2. Once the neurotransmitter is released from the terminal into the synaptic space, it interacts with postsynaptic receptors and subsequently is taken back up into the terminal via the plasma membrane transporter (e.g., the dopamine transporter, DAT and/or the serotonin transporter, SERT). Thus, transporter proteins modify the concentration of neurotransmitter in the cytosolic and vesicular storage pools, thereby having the ability to alter subsequent neurotransmission.
The present invention is directed to a method of treating an individual who suffers from drug dependence or withdrawal from drug dependence or who suffers from a disease or pathology of the CNS. The method comprises of administering to the individual an effective amount of either cis-2,6-di-trans-styrylpiperidine or trans-2,6-di-trans-styrylpiperidine or an analog thereof, including pharmaceutically acceptable salts of such compounds thereof. As used wherein, the term xe2x80x9ceffective amountxe2x80x9d means an amount of a drug effective to reduce an individual""s desire for a drug of abuse or for food, or for alleviating at least one of the symptoms of the disease or pathological symptom of CNS pathology.
The compound can be administered alone, combined with an excipient, or co-administered with a second drug having a similar or synergistic effect. The compound is administered subcutaneously, intramuscularly, intravenously, transdermally, orally, intranasally, intrapulmonary or rectally. The use of cis-2,6-di-trans-styrylpiperidine or trans-2,6-di-trans-styrylpiperidine and derivatives thereof in treating diseases or pathologies of the CNS is implicated. In particular, the treatment of dependencies on such drugs as cocaine, amphetamine, caffeine, nicotine, phencyclidine, opiates, barbiturates, benzodiazepines, cannabinoids, hallucinogens, and alcohol is implicated. Also, the treatment of eating disorders such as obesity is implicated.
In a preferred aspect of the invention, the method of treatment reduces an individual""s desire for the drug of abuse or for food by at least one day, but it is also preferred that the treatment method further comprises administering behavior modification counseling to the individual. Although the compound of the present invention is contemplated primarily for the treatment of drug abuse and withdrawal and for eating disorders, other uses are also suggested by the studies discussed herein. Thus, cognitive disorders, brain trauma, memory loss, psychosis, sleep disorders, obsessive compulsive disorders, panic disorders, myasthenia gravis, Parkinson""s disease, Alzheimer""s disease, schizophrenia, Tourette""s syndrome, Huntington""s disease, attention deficit disorder, hyperkinetic syndrome, chronic nervous exhaustion, narcolepsy, pain, motion sickness and depression, and related conditions are considered to be susceptible to treatment with a compound of the present invention.
As shown by the results of the studies described herein, cis-2,6-di-trans-styrylpiperidine and trans-2,6-di-trans-styrylpiperidine are found to be effective in inhibiting uptake of extracellular 5-HT by serotonergic nerve terminals in the CNS, as well as in inhibiting the binding of [3H]MTBZ to vesicle membranes indicating an interaction with VMAT2. These analogs are also nicotinic receptor antagonists, inhibiting nicotine-evoked [3H]DA and [3H]NE release from rat brain slices. Either or both mechanisms can thereby alter the distribution of the intracellular neurotransmitter pools, and as a result, alter extracellular neurotransmitter concentrations.
The 2,6-disubstituted piperidine analogs of the present invention include those contemplated by the following formula (I), without regard to chirality: 
wherein:
R1 represents a hydrogen, methyl, deuteromethyl (CD3), tritiomethyl (CT3), ethyl, or C3-C7 straight chain or branched alkyl (preferably methyl or ethyl), C3-C6 cycloalkyl, vinyl, allyl, C4-C7 alkenyl (including cis and trans geometrical forms), benzyl, and phenylethyl.
R2 and R3 are each independently ortho-, meta-, orpara-substituted moieties, where the substituent is described as hydrogen, methyl, ethyl, or C3-C7 straight chain or branched alkyl, C3-C6 cycloalkyl, vinyl, allyl, C4-C7 alkenyl (including cis and trans geometrical forms), benzyl, and phenylethyl. Further, the substitute moieties can be N-methylamino, N,N-dimethylamino, carboxylate, methylcarboxylate, ethylcarboxylate, propylcarboxylate, isopropylcarboxylate, carboxaldehyde, acetoxy, propionyloxy, isopropionyloxy, cyano, aminomethyl, N-methylaminomethyl, N,N-dimethylaminomethyl, carboxamide, N-methylcarboxamide, N,N-dimethylcarboxamide, acetyl, propionyl, formyl, benzoyl, sulfate, methylsulfate, hydroxyl, methoxy, ethoxy, propoxy, isopropoxy, thiol, methylthio, ethylthio, propiothiol, fluoro, chloro, bromo, iodo, trifluoromethyl, propargyl, nitro, carbamoyl, ureido, azido, isocyanate, thioisocyanate, hydroxylamino, and nitroso.
The above 2,6-substituted piperidino analogs are preferred in their 2,6-cis geometrical isomeric forms, or in their 2,6-trans geometric forms, including all possible geometric, racemic, diasteriomeric, and enantiomeric forms thereof.
The above 2,6-disubstituted piperidines as well as their analogs can be administered in their free base form or as a soluble salt. Whenever it is desired to employ a salt of a 2,6-substituted piperidine or its analog, it is preferred that a soluble salt be employed. Some preferred salts include hydrochloride, hydrobromide, nitrate, sulfate, phosphate, tartrate, galactarate, fumarate, citrate, maleate, glycolate, malate, ascorbate, lactate, aspartate, glutamate, methanesulfonate, p-toluenesulfonate, benzenesulfonate, salicylate, proprionate, and succinate salts. The above salt forms may be in some cases hydrates or solvates with alcohols and other solvents.
A pharmaceutical composition containing a compound of the invention is also contemplated, which may include a conventional additive, such as a stabilizer, buffer, salt, preservative, filler, flavor enhancer and the like, as known to those skilled in the art. Representative buffers include phosphates, carbonates, citrates and the like. Exemplary preservatives include EDTA, EGTA, BHA, BHT and the like. A composition of the invention may be administered by inhalation, i.e., intranasally as an aerosol or nasal formulation; topically, i.e., in the form of an ointment, cream or lotion; orally, i.e., in solid or liquid form (tablet, gel cap, time release capsule, powder, solution, or suspension in aqueous or non aqueous liquid; intravenously as an infusion or injection, i.e., as a solution, suspension or emulsion in a pharmaceutically acceptable carrier; transdermally, e.g., via a transdermal patch; rectally as a suppository and the like.
Generally, the pharmacologically effective dose of a present compound is in the amount ranging from about 1xc3x9710xe2x88x925 to about 1 mg/kg body weight/day. The amount to be administered depends to some extent on the lipophilicity of the specific compound selected, since it is expected that this property of the compound will cause it to partition into fat deposits of the subject. The precise amount to be administered can be determined by the skilled practitioner in view of desired dosages, side effects and medical history of the patient and the like.
The 2,6-disubstituted piperidino analogs of the present invention exhibit activity at either nAChRs and/or the serotonin transporter protein (SERT) and/or the vesicular monoamine transporter (VMAT2). 
Table 1 below summarizes the interaction of cis-2,6-di-trans-styrylpiperidine (Compound 1) and trans-2,6-di-trans-styrylpiperidine (Compound 2) with nicotinic receptors, SERT and VMAT2.
The two 2,6-disubstituted piperidino derivatives in Table 1 have the chemical structure of Formula I, and were assayed for interaction with xcex14xcex2*, xcex17*, xcex13xcex22*and xcex13xcex24*subtypes of nAChRs, interaction with VMAT2 located on vesicle membranes and inhibition of SERT function. It shall be noted that the nAChR subtypes for the activities described herein have not been elucidated conclusively, and thus, the asterisk is an indication of the putative nature of the receptor subtype mediating the action. Compound 1 exhibits good selectivity (43-fold) for the xcex13xcex22*subtype of nAChR relative to its interaction with the MTBZ site on VMAT2, as indicated by its ability to inhibit nicotine-evoked [3H]DA release. Moreover, Compound 1 exhibits very good selectivity ( greater than 370-fold) for the xcex13xcex22*and xcex13xcex24*subtypes of nAChRs compared to its interaction with either xcex14xcex22*or xcex17*subtypes of nAChR. Furthermore, Compound 1 was 770-fold more selective as an inhibitor of the xcex13xcex22*and xcex13xcex24*subtypes of nAChR compared to its inhibition of SERT function. Finally, Compound 1 interacted with VMAT2 18-fold more selectively than it inhibited the function of SERT.
Compound 2 was also assayed for interaction with nAChRs subtypes, interaction with VMAT2 located on vesicle membranes and inhibition of SERT function. Compound 2 exhibits good selectivity (9.5-fold) for the xcex13xcex22*subtype of nAChR relative to its interaction with the MTBZ site on VMAT2, as indicated by its ability to inhibit nicotine-evoked [3H]DA release. Moreover, Compound 2 exhibits very good selectivity ( greater than 24-fold) for the xcex13xcex22*subtype of nAChR compared to its interaction with either xcex14xcex22*or xcex17*subtypes of nAChR. Furthermore, Compound 2 was only 2.2-fold more selective as an inhibitor of the xcex13xcex22*subtypes of nAChR compared to its inhibition of SERT function. Finally, Compound 2 interacted with SERT 4.3-fold more selectively than it interacted with VMAT2.
Compound 1 was 18-fold more potent at inhibiting nicotine-evoked [3H]DA and [3H]NE release from rat striatal and hippocampal slices, indicated a higher affinity for the xcex13xcex22*and xcex13xcex24*subtypes of nAChRs, compared to Compound 2. On the other hand, Compound 2 was 19-fold more potent inhibiting the function of SERT than was Compound 1. Finally, Compound 1 was only 4-fold more potent interacting with VMAT2 compared to Compound 2. Thus, alteration of stereochemistry at C2 and C6 from cis to trans resulted in a diminished affinity for the xcex13xcex22*subtypes of nAChR and for VMAT2, and enhanced the affinity for SERT, whereas there was no change in affinity for either xcex14xcex22*or xcex17*subtypes of nAR. Therefore, cis-analogs have higher affinity for VMAT2 and xcex13xcex22*subtype of nAChRs.